1. Field of the Invention
The present invention pertains to a method for making a coated abrasive article, and particularly to a method for making a coated abrasive belt having an endless, spliced backing sheet reinforced by continuously applied fibrous strand or strip material, and the product of this method.
2. Description of the Related Art
Coated abrasive articles generally contain an abrasive material, typically in the form of abrasive grains, bonded to a backing by means of one or more adhesive layers. Such articles usually take the form of sheets, discs, belts, bands, and the like, which can be adapted to be mounted on pulleys, wheels, or drums. Abrasive articles can be used for sanding, grinding, or polishing various surfaces of, for example, steel and other metals, wood, wood-like laminates, plastic, fiberglass, leather, or ceramics.
The backings used in coated abrasive articles are typically made of paper, polymeric materials, cloth, nonwoven materials, vulcanized fiber, or combinations of these materials. Many of these materials alone provide unacceptable backings for certain applications because they are not of sufficient strength, flexibility, or impact resistance. As a result, early failure and poor functioning can occur, at least in certain applications of these backing materials in a nonreinforced state.
In a typical manufacturing process, a coated abrasive article, including the backing and abrasive coating, among other things, is made in a continuous web form and thereafter converted into a desired construction, such as a sheet, disc, belt, or the like. One of the most useful constructions of a coated abrasive article is an endless coated abrasive belt, i.e., a continuous loop of coated abrasive material. In order to form such an endless belt, the web form is typically cut into an elongate strip of a desired width and length. The ends of the elongate strip of the preformed sheet of coated abrasive article are then joined together to create a "joint" or a "splice".
Two types of arrangements of the free ends of an elongate discrete strip to be spliced are common in making an a spliced endless belt. These are the "lap" splice and the "butt" splice. By "lap" splice, it is meant that the two free ends of the elongate strip are respectively bevelled in a tapered manner such that the top end and the bottom end of the elongate strip can be positioned together in superposition to form a joint without causing a significant change in the overall thickness of the belt. In the lap splicing of a preformed sheet of coated abrasive article, this bevelling on the bottom end is typically accomplished by removing abrasive grains and material from the abrasive surface of the strip, and by removing part of the material from the backing or underside of the elongate strip as the top end of the splice. The bevelled ends are then overlapped and joined adhesively or mechanically.
For the "butt" splice, it is meant that the two free ends of the elongate strip are brought into a juxtaposed relationship with the end faces in confronting abutment at a juncture line for joinder. The bottom surface of the backing at each end of the elongate strip, such as a preformed sheet of coated abrasive article, typically is then coated with an adhesive, mechanical securement means or other attachment means and overlaid with a strong, thin, tear-resistant, splicing media.
However, the formation of a splice in a previously manufactured coated abrasive article sheet to provide an endless configuration thereof can be undesirable as a discontinuity is necessarily created in the abrasive coating layer at the outer surface, i.e., the abrasive coating surface, of the splice site. This type of splice is generally exemplified in U.S. Pat. Nos. 2,391,731 (Miller), 3,333,372 (Gianatsio) and 4,736,549 (Toillie). The discontinuity or splice area in the coated abrasive layer can cause a mark in a workpiece which is not consistent with the cut imparted in a workpiece surface by the unspliced remainder of the abrasive coating layer. These marks are referred to as "chatter".
Other background art includes:
U.S. Pat. No. 289,879 (Almond) pertains to a polishing tool comprising abrasive grains adhered to a tubular backing.
U.S. Pat. No. 2,012,356 (Ellis) discloses a coated abrasive having a seamless tubular fabric backing.
U.S. Pat. No. 2,404,207 (Ball) pertains to a seamless coated abrasive article having a fibrous nonwoven backing. The fibrous nonwoven backing can be saturated with an adhesive and contain other reinforcing fibers.
U.S. Pat. No. 2,411,724 (Hill) teaches a method for making an endless tubular coated abrasive, wherein a thermoplastic or thermosetting adhesive is extruded to form a backing, in which abrasive grains are embedded while the backing is molten. In another embodiment of that invention, the backing can comprise a liner of a reinforcing strands over which is the thermoplastic adhesive, which are ultimately spliced with the backing.
French Patent Application Publication No. 2,396,625 dated 2 February 1979 teaches a seamless endless coated abrasive belt that is made by the continuous weaving of a cloth backing. This published application also describes a spliced backing having a sinusoidal splice.
French Patent Publication 2,095,185 published 2 November 1972 (Ponthelet) discloses an abrasive product having a nonwoven backing which may be reinforced with filaments placed in either the transversal direction, longitudinal direction or as a grid form. Where the filaments are arranged only in one direction, the filaments are said to be maintained in a parallel arrangement as held down by a veil made of natural, artifical or synthetic fibers.
PCT Published Patent Application No. WO 93/12911 (Benedict et al.) published Jul. 8, 1993, pertains to a method of making a spliceless coated abrasive belt. The backing includes between about 40 to 99% by weight of an organic polymeric binder and an effective amount of a fibrous reinforcing material engulfed within the organic polymeric binder material. In a method of making the spliceless belt Benedict et al. includes preparing a loop of liquid binder material having fibrous reinforcing material therein around the periphery of a drum, and then solidifying the binder material to form the endless, spliceless belt.
In many abrading applications, it is desired to use an endless coated abrasive belt that has a backing with certain desired physical properties. These properties include relatively low stretch, relatively high tensile value and relatively high adhesion between the backing and the abrasive coating. Although the Benedict et al. application represents an advance in the art for making endless coated abrasive belts, there is room to explore alternate approaches to improve the physical properties of the backing.
U.S. application Ser. No. 08/079,364 filed 17 June 1993 (Schneider et al.) pertains to a method of making an endless, splice-less belt. A flowable organic material is spin casted to form an endless loop. After this spin casting, abrasive particles are inserted into the spin caster and the abrasive particles are engulfed into the organic material. The organic material is then solidified to form an endless, spliceless abrasive belt.
U.S. Pat. No. 2,349,365 (Martin et al.) involves a flexible coated abrasive article in which the backing comprises a sheet of plastic material reinforced with a sheet of cloth or paper.
U.S. Pat. No. 2,712,987 (Storrs et al.) teaches a coated abrasive in which the abrasive grains are embedded in a nylon backing. The coated abrasive containing the nylon backing, can be cut into two free ends and the two free ends joined by softening the nylon and then resolidifying.
U.S. Pat. No. 3,166,388 (Riegger et al.) discloses a coated abrasive backing comprising thermoplastic reinforcing fibers distributed throughout wood pulp fibers.
PCT published patent application No. WO 86/02306 publication dated 24 April 1986 (Hansen et al.) pertains to an improved coated abrasive backing having a flexible sheet and a multiplicity of weft free, closely spaced, stretch resistant, longitudinally aligned, coplanar, continuous filament reinforcing yarn bonded to one surface of the flexible sheet before the backing is seamed into an endless belt. However, the filament yarn is applied as a plurality of separate yarns, each of which would need to be spliced as well as the backing sheet. The filament yarn in Hansen et al. is not continuous in the sense that it continuously runs around the backing sheet from one lateral side of the backing sheet to the other. Therefore, if the abrasive article in Hansen et al. were formed into an endless configuration, the reinforcing effect of the yarn would be delimited by the strength of the spliced portion of each separate yarn.
U.S. Pat. No. 4,867,760 (Yarbrough) teaches a stitchbond fabric that consists of interlacing warp and fill yarns as a backing for coated abrasives.
U.S. Pat. No. 4,894,280 (Guthrie et al.) pertains to a flexible tear resistant sheet material comprising a web of thermoplastic microfibers with staple fibers homogeneously dispersed throughout.
U.S. Pat. No. 2,356,866 to Melton et al., and U.S. Pat. No. 2,333,035 to Oglesby disclose abrasive materials reinforced by fibrous webs.
U.S. application Ser. No. 07/903,360 (Goethel et al.) filed 24 June 1992 and assigned to the assignee of the current invention, teaches a phenolic resin for saturating a cloth backing for a coated abrasive article.